In a conventional thermal printer of the kind described, for example, in Japanese Laid Open Utility Model S63-148664 and U.S. Pat. No. 5,579,043, a roll of recording paper is installed by opening a cover, inserting the recording paper roll in the printer, and closing the cover. FIG. 10 herein is a cross section view of a portion of the thermal printer described in U.S. Pat. No. 5,579,043. When cover 213 is closed, a rubber paper drive roller 215 is set at a predetermined printing position. The paper drive roller 215 is rotatably supported by the cover 213 by means of a shaft 215a. A thermal print head 202 includes a rectangular radiation plate 206 and a ceramic substrate 203 attached to a front surface of the plate. The substrate 203 carries a row of heating points 204 which perform the printing functions. The thermal print head 202 is rotatably supported by a frame 201 through a shaft (not shown), and is pushed by a spring 209 toward the paper drive roller 215. By closing the cover 213, the paper drive roller 215 moves in the direction of an arrow Q, and recording paper 212 is pinched between the paper drive roller 215 and the thermal print head 202 at a predetermined position. During closing of the cover 213, the paper drive roller 215 first engages a tip 202a of the thermal print head 202, then moves while pushing the thermal print head 202 rearwardly, that is, toward the left, as seen in FIG. 10.
Conventional thermal printers such as that shown in FIG. 10 have some significant disadvantages. For example, the tip 202a presents to the surface of the rubber roller 215 a sharp, pointed configuration when the cover 213 is moved to the closed position. Accordingly, during closing of the cover 213, when the print drive roller 215 engages the tip 202a of the thermal print head, the tip 202a applies a concentrated impact force to the surface of the paper drive roller 215. This concentrated impact force may cause the thermo-sensitive layer of the recording paper 212 between the head 202 and the roller 215 to form colors which appear as print stains, or may damage the recording paper. This impact force may also cause deformation of the rubber paper drive roller 215. As a result, uneven print quality may occur and, in addition, the position of the substrate 203 (which carries the printing elements) may shift with respect to the radiation plate 206. Furthermore, in conventional thermal printers of the kind described, the cover may need to be pushed down a second time due to a reaction force generated when the paper drive roller 215 strikes the upper end face of the head substrate 203. As a result, the closing operation of the cover does not feel smooth to a user.
A thermal print head mechanism can be designed to permit the thermal print head to be retracted from the associated paper drive roller prior to inserting the recording paper so that the thermal print head does not contact the paper drive roller. After the recording paper is inserted in the printer, the thermal print head is returned to its position against the paper drive roller. However, such a mechanism requires the thermal print head to be first retracted from the paper drive roller and then moved back into contact with the paper drive roller. Such an operation complicates the process of replacing the recording paper.
The present invention solves the above-described problems of the prior systems. Accordingly, it is an object of the present invention to provide a thermal printer that not only eliminates stains, damage to the recording paper and deformation of the paper drive roller during closing of the printer cover but also provides smooth operation of the cover as it is moved to its closed position.